Electrolyte for the electrodeposition of technetium



United States Patent 3,374,157 ELECTROLYTE FOR THE ELECTRODEPOSITION 0F TECHNETIUM WillardD. Box, Oak Ridge, Tenn., assignor to the United States of America as represented by the Secretary of the United States Atomic Energy Commission No Drawing. Filed May 21, 1965, Ser. No. 457,872

" 2 Claims. (Cl. 204-) The present invention relates to a method and composition which permits quantitative electrodeposition of Te from an aqueous solution of sulfuric aci Technetium-99 is a low energy beta emitter, with a simple decay scheme, decaying to the stable ruthenium- 99 isotope. Among other areas of utility the soft beta (0.29 mev.) rays of Tc99 can be used to hasten blood coagulation in eye surgery to minimize scar formation. Other areas of utility are as beta calibration sources and as static eliminators. To be useful for any of these or similar purposes, it is usually necessary to provide the Te as a thin-layered adherent deposit on a metallic substrate. It is also preferable that the To deposit be of high purity and the yield of Tc metal as deposited from a given plating solution be high, By high yield, I'mean that in excess of 99% of the Tc in solution can be electrodeposited as a thin, smooth, adherent layer on a cathode surface within a reasonably short time.

The present invention meets this objective by providing for the electrodeposition of Te from an electroplating solution comprising an aqueous solution of sulfuric acid containing dissolved technetium, as pertechnetate ion, and a polycarboxylic acid selected from oxalic acid, citric acid, tartaric acid, glutaric, malonic, succinic, and ammonium salts thereof.

Electroplating of technetium from a pertechnetate solution of sulfuric acid is known. Thus, for example, I. D. Eakins and D. G. Humphries have reported in the Journal of Inorganic Nuclear Chemistry, vol. 25 (6) 2737 (1963) the electrolytic deposition of Te from a solution of ammonium pertechnetate in 2 M sulfuric acid. It was found that deposition of technetium was terminated after only a quarter of the total technetium in solution had been deposited, with the remainder having been converted to an insoluble form.

In accordance with the present invention an electrolytic bath is provided from which technetium can be electroplated with virtually total yield efiiciency as a smooth, adherent deposit on the surface of a selected metal substrate. The improved electrolytic bath comprises an aqueous solution of sulfuric acid containing pertechnetate as ammonium pertechnetate and a pertechnetate stabilizing agent selected from oxalic acid, citric acid, tartaric acid, glutaric, malonic, succinic, and ammonium salts thereof. I use the term technetium stabilizing agent in the sense that the oxalate or other polycarboxylic acid of the defined class apparently retains the technetium in pertechnetate form and prevents reduction to lower valence states as evidenced by precipitate formation.

The preparation of the electrolytic bath is efliected by dissolving ammonium pertechnetate in an aqueous solution of the free acid or in the ammonium salt form of the selected pertechnetate stabilizing agent. A preferred solution is ammonium pertechnetate dissolved in at least 0.4 M ammonium oxalate to which sufiicient sulfuric acid is added to reach a solution pH in the range 1 to 2. The hydrogen ion concentration in solution in combination With the material used as cathode, will determine whether the technetium plates are used as metal or as an oxide.

By placing the aforementioned technetium solution in a tank such as a glass vessel containing a platinum gauze anode facing a selected metal foil or sheet as cathode, and joining the cathode and anode through an external DC 3,374,157 Patented Mar. 19, 1968 power supply, electroplating of Te as metal or oxide can be effected. I have found that a 0-20 volt, O-20 amp. 400 watt DC source will furnish suflicient current to effect electrodeposition.

The following examples will illustrate the efficiency of the novel electroplating bath, as well as pointing out the operational and preferred parameters.

Example I In this example To was electroplated from 3 separate solutions each consisting of ml. of a solution of ammonium pertechnetate containing 0.7 M oxalate, each of said solutions being adjustedto 0.45 in sulfuric acid. A copper cathode and a platinum gauze anode was used in electroplating the Te. The copper cathode was weighed before and after Tc deposition. Plating was effected at room temperature (25 C.) using a cathode current den sity in the range 1.0 to 1.3 amp/cm. to'produce a smooth adherent deposit. Higher deposition rates or higher plating temperatures tend to produce less adherent deposits. The electrolysis was continued until no further weight gain was detected on the cathode. The weight of the Tc dissolved in the solution, the amount of Tc deposited and the percent yield is listed below in Table I.

TABLE I Run No. 7 To in Electrolyte, mg. Te deposited, mg. Yield, Percent 1 25 24. 86 99. 6 2 9. 81 9. 73 99. 2 3 6.56 6.53 99. 6

It will be seen that in each run substantially all of the technetium in solution was deposited on the cathode. By contrast, the technetium deposition yield efficiency from solutions which did not contain the technetium stabilizing oxalate reagent reached a value of about 25%, whereupon the dissolved technetium precipitated and further deposition ceased. Examination of any of the metallic deposits under a high-power microscope showed the technetium metal deposited on the cathode surface as microscopic spheres (ranging from 0.00008 to 0.00007 inch in diameter) built up in layers. By wiping the surface of the deposit with light tissue paper several times any loose technetium can be removed so that a background reading of less than 10 disintegrations per. minute is reached in the third to fifth wiping. The technetium surfaced element is then ready for use for any of the aforementioned or similar purposes.

Example II Example III This example shows how process varied to yield a technetium metal desired.

According to this invention, technetium may be plated as metal of oxide depending on the concentration of technetium stabilizing reagent and sulfuric acid in solution. For example, using a fixed amount (0.7 M) oxalate as the technetium stabilizing reagent and a copper cathode, the minimum acid concentration was 0.45 M; with platium as the cathode the minimum acid concentration parameters may be or oxide deposit, as

3 necessary to obtain a Tc metal deposit was 1.90 M. The various metals used as cathodes and the acid concentrations for metal and oxide deposition are listed in Table II below using a constant oxalate concentration of 0.7 M.

, The oxalate concentration necessary in the electrolyte for the Te metal-or oxide deposition depends on the acid concentration in solution. For example, when copper is the cathode and electrodeposition is effected from a solution 0.4 M in oxalate, an acid concentration of 1.90 M

will yield a technetium oxide deposit. When the oxalate concentration is increased to 0.7 M a technetium metal deposit With an acid concentration of only 0.45 M is formed. As a matter of convenient operation, I prefer to use a saturated solution of the technetium stabilizing reagent, while varying the acid concentration according to whether a metal or oxide deposit is desired.

It will be seen that I have described a novel electroplating bath for use in the eflicient electrodeposition of technetium to form a smooth, adherent deposit on a metal substrate. The invention has been described and illustrated in use with an oxalate salt as the technetium stabi- 4 lizing reagent. However, it should be understood that the same general order of plating etficiency Will be realized when practicing the invention With the class of polycarboxylic acids and ammonium salts previously defined.

Having thus described my invention, I claim:

1. An electrolytic plating bath for technetium comprising an aqueous solution of sulfuric acid containing technetium as pertechnetate ion, and a stabilizing amount of a polycarboxylic acid selected from the group consisting of oxalic, gluatric, malonic, succinic, tartaric, and citric acids and ammonium salts thereof, sufiicient to prevent reduction of the pertechnetate in solution to a lower oxidation state, said bath having a pH in the range of 1 to 2.

2. The electrolytic plating bath recited in claim 1 in which the pertechnetate stabilizing reagent is ammonium oxalate.

References Cited UNITED STATES PATENTS 2,497,725 2/1950 Griffith 204-105 OTHER REFERENCES Journal of Inorganic and Nuclear Chemistry, vol. 25, No. 6, pp. 737-739, June 1963.

Radioisotopes, vol. 8, No. 1, pp. 32-33, March 1959.

The Journal of Chemical Physics, vol. 13, No. 6, pp. 269-276, July 1945.

HOWARD S. WILLIAMS, Primary Examiner.

G. KAPLAN, Assistant Examiner. 

1. AN ELECTROLYTIC PLATING BATH FOR TECHNETIUM COMPRISING AN AQUEOUS SOLUTION OF SULFURIC ACID CONTAINING TECHNETIUM AS PERTECHNETATE ION, AND A STABILIZING AMOUNT OF A POLYCARBOXYLIC ACID SELECTED FROM THE GROUP CONSISTING OF OXALIC, GLUATRIC, MALONIC, SUCCINIC, TARTARIC, AND CITRIC ACIDS AND AMMONIUM SALTS THEREOF, SUFFICIENT TO PREVENT REDUCTION OF THE PERTECHNETATE IN SOLUTION TO A LOWER OXIDATION STATE, SAID BATH HAVING A PH IN THE RANGE OF 1 TO
 2. 